Practice Empirical Formula in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The chemical formula that shows the simplest whole-number ratio of atoms of each element present in a compound, obtained by dividing all subscripts by their.

The reduced fraction of atoms—smallest numbers that show the ratio.

Showing a random 20 of 50 problems.

Example 1

easy
A compound contains 0.20 mol0.20\,\text{mol} Na and 0.20 mol0.20\,\text{mol} Cl. What is its empirical formula?

Example 2

medium
A hydrocarbon is 80% C and 20% H by mass. Find its empirical formula (C=12, H=1).

Example 3

medium
A compound is 75% C and 25% H by mass. Find the empirical formula (C=12, H=1).

Example 4

easy
What is the empirical formula of C4H10?

Example 5

challenge
Combustion of a hydrocarbon gives 0.6 mol CO2 and 0.6 mol H2O. Find the empirical formula.

Example 6

medium
A compound is 50.0%50.0\% S and 50.0%50.0\% O by mass. Find its empirical formula (S =32= 32, O =16= 16).

Example 7

easy
A compound is found to have a mole ratio of N : O = 1 : 2. What is its empirical formula?

Example 8

medium
A compound's molecular formula is C6H12O6\text{C}_6\text{H}_{12}\text{O}_6. Find its empirical formula.

Example 9

medium
If percent composition gives moles in a ratio C:H:O = 1.0 : 2.0 : 0.5, what whole-number ratio do you use?

Example 10

medium
A sample contains 24 g of carbon and 8 g of hydrogen. Find its empirical formula (C=12, H=1).

Example 11

hard
A hydrocarbon has empirical formula CH\text{CH} and molar mass 78 g/mol78\,\text{g/mol}. Identify the molecular formula.

Example 12

hard
If a sample yields a 1 : 1.33 mole ratio, what factor brings it to whole numbers?

Example 13

easy
What is the empirical formula of acetylene, C2H2\text{C}_2\text{H}_2?

Example 14

hard
A compound has empirical formula CH2O\text{CH}_2\text{O} and a molar mass of 180 g/mol180\,\text{g/mol}. Find the molecular formula.

Example 15

easy
Is the empirical formula of H2O\text{H}_2\text{O} equal to its molecular formula?

Example 16

easy
Fill in the blank: an empirical formula shows the ____ whole-number ratio of atoms.

Example 17

challenge
A compound is 43.7% P and 56.3% O by mass. Find the empirical formula (P=31, O=16).

Example 18

hard
An oxide of iron has 69.9%69.9\% Fe and 30.1%30.1\% O by mass. Find the empirical formula (Fe =56=56, O =16=16).

Example 19

easy
What is the empirical formula of C6H6 (benzene)?

Example 20

medium
A compound is 40.0%40.0\% carbon, 6.7%6.7\% hydrogen, and 53.3%53.3\% oxygen by mass. What is its empirical formula?
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